I have RX480 sapphire nitro+ 8gb. I always use latest updates. 1 week ago i saw my GPU is going 75 degrees idle when PC was just on desktop.. Normally runs 45-50. I tried to update my drivers but nothing happened.. then i tried to use older drivers and i fix the problem for a few days. But always when restart my PC the problem comes again... Today i tried again to change the drivers and tried both old and new drivers. After driver installation they want to restart my PC but i tried to postpone it for 1-2 hours and before the restart everything was fine.. my GPU was running perfect, but when i restarted my PC again to full complete driver installation.... 75 degrees just 1-2 mins after reboot.. My PC is 1 year old, intel i5 7600 3.5-4.0 Ghz, 16gb ram DDR4 and AMD Radeon RX 480 Sapphire Nitro + 8gb DDR5 GPU.

I appreciate the information you did give, it still isn't enough for help on this effectively. Really need to know what OS and version you are running. I'd also like to know what driver are you calling the latest? 18.3.3?

I have a thought that if your are running Windows 10 you may want to try disabling Windows 10 Fast Startup. You can google this. Sometimes it pulls old information from and old file. Disabling this make it start fresh every time and with the current drivers.

When the Rx480 is running hot at idle, is the card running at maximum rate? Are you by any chance using a 3rd party software like MSI Afterburner or Asus Tweak II or Trixx? If you are uninstalled them and see if it makes any difference.

You can also try this solution from a previous thread. Seems like Relive tends to cause RX series GPU card to run at maximum at times. They basically ended the RELIVE task in Task manager. Afterwards the GPU went back to normal.